1. Field of the Invention
This invention relates to a ball valve, and more particularly, to a ball valve comprising a valve body, a ball set in the valve body and a seat carrier located on at least one side of the ball, in the valve body, to carry a seat to hold the ball in position within the valve body. The seat carrier is detachably fixed in the valve body.
2. Description of the Prior Art
Ball valves are already known in the prior art. The known ball valves comprise of valve body, a stem, a ball, seats, a pair of seat carriers, connecting sleeves and union nuts. The valve body has a cylindrical hole extending therethrough which forms the valve chamber. The stem extends laterally into the central portion of the valve body, with one end thereof projecting into the valve chamber. The ball has a bore diametrically extending therethrough and is inserted in the valve chamber and engages the end of the stem such that it is rotatably held in the valve chamber. The ball must be able to be inserted into the valve body for assembling, and for this purpose the ball has a groove on the top thereof to receive and engage the end of the stem. Thus, the ball can be removed from the valve body when the ball is turned sideways, that is, in the state when the bore crosses the valve chamber in the valve body i.e., in the closed position.
A seat carrier is located on at least one side of the ball and, usually two seat carriers are located one on each side of the ball. The seat carrier is provided with a ball seat on the end facing to the ball in close contact with the ball to set the ball in position and to allow the ball to rotate freely. If the ball seat is abraded by the rotation of the ball, after a period of use and a gap may be formed between the ball seat and the ball. The seat carrier is designed to be able to move towards the ball in the valve body to eliminate the gap. Thus, most of the conventional ball valves have not been designed to firmly secure the seat carrier to the valve body.
In order to prevent the seat carrier from moving out of the valve body, a connecting sleeve is provided in contact with the seat carrier and joined to the valve body by a union nut. Thus the ball seat is pressed against the ball via the seat carrier and the connecting sleeve by the force exerted by the union nut and this prevents the ball from coming out of the valve body. Therefore, if the ball seat is worn, it gives rise to play between the ball and the seat, and then the union nut must be further rotated to advance the connecting sleeve inwardly to bring the ball seat into close contact with the ball.
The above described ball valve, however, has serious drawbacks in that the union nut joined on the down side of the valve cannot be removed from the valve body while fluid pressure is being maintained More particularly, it is sometimes required that a pipe connected on the downstream of the valve be replaced or repaired while the valve is in use. In such cases, the valve is closed and the union nut on the downstream side is removed, the ball however, comes out of the valve body together with the seat carrier because of the fluid pressure in the line, and hence it may result in bodily injury and/or a great deal of fluid flowing out of the line. These drawbacks result from the necessity that the seat carrier must be movable in the valve body in the axial direction thereof and that the ball, when turned sideways, i.e., in the closed position, must be detachable from the stem in order that the valve can be assembled.
In order to overcome the above drawbacks, U.S. Pat. No. 4,059,250 suggests that the seat carrier be directly fixed to the valve body. This is accomplished using a bayonet means, wherein, the seat carriers are provided with partial projections on the outer surface thereof, and the valve body, at each end thereof, is provided with recesses and grooves on the inner wall surface thereof. The projections are inserted into the recesses and then set in the grooves. More particularly, the seat carriers are provided with the projections, that is dogs, on the outer surface at one end thereof and, the valve body is cut-away from both ends towards the inner portion thereof to form recesses and grooves on the inner wall surface thereof and to form lips on the remaining surface. The projections are mated with the recesses, and the seat carriers are inserted into the valve body and then rotated to fit the projections in the grooves. Thus by engaging the projections with the lips, the seat carriers are fixed to the valve body.
Using the bayonet means, the seat carriers are fixed to the valve body immediately after having been inserted and rotated. However, sometimes the seat carriers are rotated back and as a result, the seat carrier may come out of the valve body. Thus, U.S. Pat. No. 4,059,250 suggests that a wedge be inserted between the seat carrier and the valve body to prevent the seat carrier from rotating back in the valve body.
The formation of the grooves in the valve body, as suggested by the U.S. Pat. No. 4,059,250, however, has the disadvantage that the thickness of the valve body is partially reduced and this results in a decrease in strength or pressure resistance. Thus, in order to maintain the original pressure resistance, the thickness of the entire valve body must be increased, which results in the disadvantage that the valve, as a whole, increases in weight and further, the cost of manufacturing is increased. In spite of the apparent disadvantages, U.S. Pat. No. 4,059,250 suggests the formation of the grooves in the valve body, and this is due to the thought that there is no other way for fixing the seat carrier to the valve body. In other words, the prior art patent is based on the idea that, if projections are provided on the inner surface of the valve body, the projections would hinder insertion of the ball when the valve is to be assembled, and that the grooves should be formed on the valve body in order to avoid the hindrance to the insertion. The present invention aims to overcome this problem in the prior art.
Further, in U.S. Pat. No. 4,059,250, the insertion of the wedge between the seat carrier and the valve body also has disadvantages. In particular, the wedge is small and may be lost when the valve is disassembled or forgotten when the valve is assembled. When the used valve is to be repaired, most workers who assemble the valve do not know particular structures of the valve and they are liable to fail to insert the wedge in the valve. Furthermore, the wedge is very small and thus it is difficult to insert. If the wedge is not inserted, the seat carrier may rotate backwards when the union nut is removed, and the seat carrier may come out of the valve body and simultaneously the ball may come out. The present invention eliminates these disadvantages.